1. Field of the Invention
The present invention relates to a method for manufacturing an alloy consisting of two or more metal elements and, more particularly to a method wherein an arc is generated between pairs of single metal electrodes to manufacture the alloy.
2. Description of the Prior Art
In general, titanium alloy, as a structural material, is manufactured by a method wherein sponge titanium is mixed with other metal elements, and then is compacted into a consumable electrode. This electrode is melted, by means of a vacuum arc furnace. Thus, titanium alloy is obtained. In the case of manufacture of Nb-Ti alloy, however, if the Nb content is 10 wt.% or more, compacting of Nb will become impossible. Therefore, Nb-Ti alloy containing 50 wt% or more Nb, used for superconductive fine wire, is manufactured as an ingot by a method wherein:
(1) Firstly, Ti-sheet and Nb-sheet are cut to form a joined shape meeting a designated metal composition, and then, those multiple cut pieces are combined into melting materials: PA1 (2) Those melting materials are set as consumable electrodes in a vacuum arc furnace, and then, an arc is generated between the melting materials and the mold. Through this process, the melting materials, as consumable electrodes, are cast into an ingot by melting in the mold; and PA1 (3) A plurality of these ingots are firmly welded to form a block. This block is remelted, as a consumable electrode, in a vacuum arc furnace. PA1 providing a pair of spaced apart consumable electrodes, each electrode consisting of the same single metal element, and arranging a plurality of pairs of said electrodes, the single metal element of each pair being different from one another; generating an arc between the two consumable electrodes of each of said plurality of pairs of electrodes in a non-oxidizing atmosphere, to cause the two consumable electrodes of each pair to be melted at the ends of each of the two consumable electrodes which face each other; and collecting molten drops produced by the melting in a mold to form a molten metal in the mold, the molten metal being cast into an alloy consisting of two or more of said single metal elements.
This method, however, is disadvantageous in that, since a melting electrode with a desired metal composition has to be prepared in advance, the production costs are high and still, the operational efficiency low. In other words, because Nb-sheet and Ti-sheet are cut to meet predetermined sizes, the yield ratio goes down. In addition to the high price of the metal, this low yield increases the production cost. Further, since the Ni-sheet and Ti-sheet are welded together, the work becomes so complicated that the work efficiency is quite impaired. Materials in the process also are in danger of being polluted by the atmosphere of the welding or the electrode of the welder.
Moreover, in this method, Niobium and Titanium are hard to homogeneously melt. Nb has a melting point higher than that of Ti by approximately 800.degree. C. Owing to this, when the Nb-sheet and Ti-sheet are melted by an arc as an electrode, a phenomenon that titanium with lower melting point is preferentially melted occurs. Resultantly, without normal melting of Nb-sheet, small unmelted pieces of the Nb-sheet often drop into a mold. Then, the small pieces are so hard to be melted in the molten bath of Nb-Ti alloy contained in the mold being cooled that they remain unmelted in the state of being caught on the surface of the solidification boundary. Those remaining pieces are not melted in the following second and third melting processes even though they are so minute as 1 mm or less. Those pieces exist in a final ingot and become defects.
A a kind of vacuum arc furnace method, is disclosed in Japanese Patent Application Laid Open (KOKAI) No. 165271/80, wherein two melting materials workable as electrodes are horizontally and parallelly positioned to allow an arc to be generated between the two electrodes. The electrodes are thereby melted, and molten drops of the electrodes are cast directly into a mold. This method, however, has a requirement that its electrodes are made of an alloy produced in advance, and, in this point, is different from the present invention.